Disaster Flood Scenario: Case Study of the Uh River at Lekárovce (Slovakia)

The occurrence of extreme floods in several river basins of the countries of Central and Eastern Europe over the last thirty years has drawn the attention of the public (as well as the competent authorities) to the problems of flood protection. Although the development and operational use of non-structural measures (such as flood forecasting and warning systems), represents one of the effective flood protection measures, the structural means (flood protection, levees, flood control reservoirs) are of great importance, too. Especially in the upper parts of the river basin, where the time between the detection of the causes of the flood (heavy rainfall) and its consequence (flood) is short and does not affect the effective protective activity (e.g. evacuation). Over the last 30 years, flood protections have been built along the Uh River (Slovakia, Ukraine) to protect the environment from floods. These dams adversely affected the storage capacity of water in the basin. This resulted in flood flows increase on the lower sections of the Uh River in Slovakia. These facts need to be demonstrated by the need to evaluate the proposed design values for those sections. The study presents an analysis of the long-term flood regime of the river Uh in the section Uzhhorod (Ukraine) - Lekárovce (Slovakia). The first part analyses the trend changes in the time series of maximum annual discharge Qmax in the stations Lekárovce and Uzhhorod on the basis of the observed Qmax data in these profiles (period 1931-2019). These Qmax series were subsequently used to estimate the maximum T-year discharge at the Lekárovce station for the changed conditions of the Uzhhorod - Lekárovce section. Using these derived data and the observed form of the summer flood hydrograph from July 1980, a 100-year flood scenario was developed for the Uh River in Lekárovce. The achieved results indicate a further increase in flood risk in Lekárovce.

The Role of Frost Processes in the Retreat of River Banks

The rate of bank retreat was measured using erosion pins on the alluvial banks of the rivers in the Podhale region (the boundary zone between Central and Outer Carpathians) during the hydrological year 2013/2014. During the winter half-year (November–April), the bank retreat was mainly caused by processes related to the freezing and thawing of the ground (swelling, creep, downfall). During the summer half-year (May–October), fluvial processes and mass movements such as lateral erosion, washing out, and sliding predominated. The share of fluvial processes in the total annual amount of bank retreat (71 cm on average) was 4 times greater than that of the frost phenomena. Erosion on bank surfaces by frost phenomena during the cold half-year was greatest (up to 38 cm) on the upper parts of banks composed of fine-grained alluvium, while fluvial erosion during the summer half-year (exceeding 80 cm) mostly affected the lower parts of the banks, composed of gravel. The precise calculation of the relative role of frost phenomena in the annual balance of bank erosion was precluded at some stations by the loss of erosion pins in the summer flood.

TO THE QUESTION OF COMPREHENSIVE ASSESSMENT OF SURFACE WATER IN THE CENTRAL CAUCASUS DURING WINTER BETWEEN AND SUMMER FLOOD

Based on long-term observations, the assessment of the pollution of the rivers of the Central Caucasus was carried out by comparing the calculated coefficients of the complexity of pollution and the specific combinatorial index of pollution of surface waters, and the quality classes were determined. The results of chemical analysis of the concentration levels of trace impurities (Mo, Pb, Zn, V, Ni, Cr, Mn, Ag) and inorganic nitrogen compounds (NO2 -, NO3 — and NH4 +) in the waters of 13 rivers in two permanent sections of each watercourse were used. The results of calculating the indicators of pollution in the waters of rivers of winter low water and summer high water are presented. The most polluted watercourses and the frequency of pollution in each river are identified, estimated by the values of the specific combinatorial index of water pollution, the coefficient of complexity of pollution, and the class of water quality is presented. The assessment of the most polluted water bodies during the winter low-water period and summer flood is given according to the classification of water quality. According to long-term observations, the features of watercourses and their differences in terms of pollution are presented.

The Dessau Grassland Experiment—Impact of Fertilization on Forage Quality and Species Assembly in a Species-Rich Alluvial Meadow

Since alluvial meadows of river valleys of the Cnidion dubii are protected by the EU Habitats Directive, reconciling farmers’ demands for forage quality with the objective of maintaining them in good conservation status is an important issue in grassland research. In a long-term experiment from 2010 to 2018, we investigated the impact of fertilizing on forage quality and species assembly on a species-rich and twice-mown alluvial grassland in the Dessau Elbe floodplain (Germany). The experiment was composed of an unfertilized control, PK, N60, N60PK and N120PK applications. A significant improvement in forage quality was achieved by nitrogen fertilization only for crude protein, with higher feeding requirements for sheep met only in individual years. The legume cycle was inhibited by the application of nitrogen and high grass cover was maintained, but not increased, at the highest nitrogen application after an exceptional summer flood. The target forbs persisted in numbers over the study period in all treatments. For cover, the low-competitive target forbs responded neutrally to nitrogen fertilization, whereas detrimental effects were demonstrated for the competitive ones. Thus, we recommend not applying more than 60 kg year−1 of nitrogen and only in combination with phosphorus and potassium.

Effect of a Summer Flood on Benthic Macroinvertebrates in a Medium-Sized, Temperate, Lowland River

Floods are naturally occurring extreme hydrological events that affect stream habitats and biota at multiple extents. Benthic macroinvertebrates (BM) are widely used to assess ecological status in rivers, but their resistance and resilience to floods in medium-sized, temperate, lowland rivers in Europe have not been sufficiently studied. In this study, we quantified the effect of a moderate (5-year return period) yet long-lasting and unpredictable flood that occurred in summer 2020 on the BM community of the Jeziorka River in central Poland. To better understand the mechanisms by which the studied flood affected the BM community, we also evaluated the dynamics of hydrological, hydraulic, channel morphology, and water quality conditions across the studied 1300 m long reach. Continuous water level monitoring, stream depth surveying, and discharge measurements. As well, in-situ and lab-based water quality measurements were carried out between March and August 2020. BM communities were sampled three times at eight sites along the reach, once before and twice after the flood. High flow velocities during the flood resulted in stream bed instability leading to sand substrate movement that caused streambed aggradation by up to 0.2 m. Dissolved oxygen and ammonium-nitrogen were major drivers of BM community structure. Taxa richness, abundance, and the BMWP-PL index declined significantly, whereas Shannon evenness and Simpson diversity indices showed no significant change in the first post-flood sampling, as indicated by Kruskal–Wallis and Tukey tests. Non-metric multidimensional scaling (NMDS) analysis showed that community composition was also significantly affected by the flood. Seven weeks after the flood peak (August 2020 sampling), BM communities had fully recovered from the disturbance. The results can serve as a first approximation of the resistance and resilience of BM communities for relevant applications in other medium-sized, low-gradient, temperate rivers.

Effect of a Once in 100-Year Flood on a Subtropical Coastal Phytoplankton Community

Subtropical systems experience occasional severe floods, dramatically altering the phytoplankton community structure, in response to changes in salinity, nutrients, and light. This study examined the effects of a 1:100 year summer flood on the phytoplankton community in an Australian subtropical bay – Moreton Bay – over 48 weeks, from January to December 2011. Immediately after maximum flood levels were reached on the rivers flowing into the bay, the lowest salinity, and highest turbidity values, in more than a decade, were measured in the Bay and the areal extent of the flood-related parameters was also far greater than previous flood events. Changes in these parameters together with changes in Colored Dissolved Organic Matter (CDOM) and sediment concentrations significantly reduced the light availability within the water column. Despite the reduced light availability, the phytoplankton community responded rapidly (1–2 weeks) to the nutrients from flood inputs, as measured using pigment concentrations and cell counts and observed in ocean color satellite imagery. Initially, the phytoplankton community was totally dominated by micro-phytoplankton, particularly diatoms; however, in the subsequent weeks (up to 48-weeks post flood) the community changed to one of nano- and pico-plankton in all areas of the Bay not usually affected by river flow. This trend is consistent with many other studies that show the ability of micro-phytoplankton to respond rapidly to increased nutrient availability, stimulating their growth rates. The results of this study suggest that one-off extreme floods have immediate, but short-lived effects, on phytoplankton species composition and biomass as a result of the interacting and dynamic effects of changes in nutrient and light availability.

MONITORING THE LEVEL OF HEAVY METAL COMPOUNDS IN THE TEREK RIVER

В статье представлен анализ многолетних результатов (2005-2020 годы) изменчивости уровня содержания соединений таких тяжелых металлов как хром, никель, молибден, свинец, цинк и марганец. Цель исследования - выявление и оценка степени загрязненности воды реки Терек растворенными формами металлов в среднем и нижнем течении в летнее половодье по частоте превышения ПДК. The article presents an analysis of long-term results (2005-2020) of variability in the content of compounds of such heavy metals as chromium, nickel, molybdenum, lead, zinc and manganese. The purpose of the study is to identify and assess the degree of water pollution of the Terek River by dissolved forms of metals in the middle and lower reaches during the summer flood in terms of the frequency of exceeding the MPC.